Lucas didn't make this an official announcement, so to make sure everyone saw it:
By popular demand, Alembic is now officially checked into GitHub, which should be considered the main repository:
https://github.com/alembic/alembic
For the time being, we plan on keeping the source code for releases checked into Google Code as well, since we know many of have invested time in your clones of the project:
https://code.google.com/p/alembic/
We are in the process of transitioning the various links and documentation over to GitHub, so you will see those references update over time.
As mentioned, if you want to submit a github pull request, make sure you, or your company, has signed the Alembic Contributor License Agreement which can be found here:
https://code.google.com/p/alembic/wiki/Downloads?tm=2
As always, we welcome your feedback and thank you for the interest and support you've shown the Alembic project over the years!
Francois.